Abstract 315

Davison,-TM; Cowan,-RT; Shepherd,-RK; Martin,-P

Queensland Dep. Primary Industries, Kairi Research Station, Kairi, Qld. 4872, Australia.

Australian-Journal-of-Experimental-Agriculture-and-Animal-Hu bandry. 1985, 25: 3, 505-514; 23 ref.

In a 3-year experiment in Queenland on Gatton panic (Panicum maximum cv. Gatton) pastures 32 Friesian cows were kept at 4 stocking rates (2.0, 2.5, 3.0 and 3.5 cows/ha), each at 2 rates of fertilizer application, nitrogen 200 and 400 kg/ha year. The higher rate of fertilization increased the pasture green DM (P <0.01) by 1106 kg/ha in summer and 548 kg/ha in spring. Green DM decreased (P <0.01) with increasing stocking rate, with mean yields of 3736 and 2384 kg/ha at 2.0 and 3.5 cows/ha, respectively. Crude protein content of leaf increased stocking rate and amount of applied N fertilizer. Values ranged from 12.1 to 26.5% of DM in leaf and from 3.7 to 13.8% DM in stem. In leaf, sodium concentration (range 0.05 to 0.20% DM) was increased and phosphorus concentration (range 0.21 to 0.44% DM) was decreased by the higher rate of fertilizer application. Plant Na and P were inadequate for high levels of milk production. Dietary leaf content and crude protein contents were consistently increased by a reduced stocking rate and the higher rate of fertilization. Cows were able to select for leaf and at the lowest stocking rate, leaf in the diet was 38%; leaf content of the pasture was 20%. Dietary leaf content ranged from 38 to 57% in summer and from 11 to 36% in winter. Dietary crude protein ranged from 13 to 15% in summer and from 7 to 11% in winter and was positively correlated with pasture crude protein content and dietary leaf percentage. Soil pH decreased (P <0.05) from an overall mean of 6.3 in 1976 to 6.1 at N 200 and 5.8 at N 400 kg/ha in 1979. Soil P status remained stable; Ca and magnesium were lower (P <0.01) after 3 years.